@article{Wang2019,
title = {Adaptive Scan for Atomic Force Microscopy Based on Online Optimisation: Theory and Experiment},
author = {K. Wang and M. G. Ruppert and C. Manzie and D. Nesic and Y. K. Yong},
year = {2019},
date = {2019-01-31},
journal = {IEEE Transactions on Control System Technology},
abstract = {A major challenge in Atomic Force Microscopy
(AFM) is to reduce the scan duration while retaining the
image quality. Conventionally, the scan rate is restricted to a
sufficiently small value in order to ensure a desirable image
quality as well as a safe tip-sample contact force. This usually
results in a conservative scan rate for samples that have a
large variation in aspect ratio and/or for scan patterns that
have a varying linear velocity. In this paper, an adaptive scan
scheme is proposed to alleviate this problem. A scan line-based
performance metric balancing both imaging speed and accuracy
is proposed, and the scan rate is adapted such that the metric
is optimised online in the presence of aspect ratio and/or linear
velocity variations. The online optimisation is achieved using an
extremum-seeking (ES) approach, and a semi-global practical
asymptotic stability (SGPAS) result is shown for the overall
system. Finally, the proposed scheme is demonstrated via both
simulation and experiment.},
note = {accepted for publication},
keywords = {AFM, Nanopositioning, SPM, System Identification, Tracking Control},
pubstate = {published},
tppubtype = {article}
}

A major challenge in Atomic Force Microscopy
(AFM) is to reduce the scan duration while retaining the
image quality. Conventionally, the scan rate is restricted to a
sufficiently small value in order to ensure a desirable image
quality as well as a safe tip-sample contact force. This usually
results in a conservative scan rate for samples that have a
large variation in aspect ratio and/or for scan patterns that
have a varying linear velocity. In this paper, an adaptive scan
scheme is proposed to alleviate this problem. A scan line-based
performance metric balancing both imaging speed and accuracy
is proposed, and the scan rate is adapted such that the metric
is optimised online in the presence of aspect ratio and/or linear
velocity variations. The online optimisation is achieved using an
extremum-seeking (ES) approach, and a semi-global practical
asymptotic stability (SGPAS) result is shown for the overall
system. Finally, the proposed scheme is demonstrated via both
simulation and experiment.

Atomic force microscope (AFM) cantilevers with integrated actuation and sensing provide several distinct advantages over conventional cantilever instrumentation. These include clean frequency responses, the possibility of down-scaling and parallelization to cantilever arrays as well as the absence of optical interference. While cantilever microfabrication technology has continuously advanced over the years, the overall design has remained largely unchanged; a passive rectangular shaped cantilever design has been adopted as the industry wide standard. In this article, we demonstrate multimode AFM imaging on higher eigenmodes as well as bimodal AFM imaging with cantilevers using fully integrated piezoelectric actuation and sensing. The cantilever design maximizes the higher eigenmode deflection sensitivity by optimizing the transducer layout according to the strain mode shape. Without the need for feedthrough cancellation, the read-out method achieves close to zero actuator/sensor feedthrough and the sensitivity is sufficient to resolve the cantilever Brownian motion.

Atomic force microscope cantilevers with integrated actuation and sensing on the chip level provide several distinct advantages over conventional cantilever instrumentation. These include clean frequency responses, the possibility of down-scaling and parallelization to cantilever arrays as well as the absence of optical interferences. However, the two major difficulties with integrated transduction methods are a complicated fabrication process, often involving a number of fabrication
steps, and a high amount of feedthrough from actuation to sensing electrodes. This work proposes two hybrid cantilever designs with piezoelectric actuators and piezoresistive sensors to reduce the actuator to sensor feedthrough. The designs can be realized using a commercial microelectromechanical systems fabrication process and only require a simple five-mask patterning and etching process. Finite element analysis results are presented to obtain modal responses, actuator gain and sensor sensitivities of the cantilever designs.

@inproceedings{Moore2018,
title = {Arbitrary placement of AFM cantilever higher eigenmodes using structural optimization},
author = {S. I. Moore and M. G. Ruppert and Y. K. Yong},
year = {2018},
date = {2018-07-04},
booktitle = {International Conference on Manipulation, Automation and Robotics at Small Scales (MARSS)},
journal = {International Conference on Manipulation, Automation and Robotics at Small Scales (MARSS)},
abstract = {This article presents a novel cantilever design approach to place higher mode frequencies within a specific frequency band to alleviate instrumentation and Q control feasibility. This work is motivated by the emerging field of multifrequency atomic force microscopy (AFM) which involves the excitation and/or detection of several cantilever modes at once. Unlike other operating modes, multifrequency AFM allows the tracking of the sample topography on the fundamental mode while simultaneously acquiring complimentary nanomechanical information on a higher mode. However, higher modes of conventional rectangular tapping-mode cantilevers are usually in the MHz regime and therefore impose severe restrictions on the direct controllability of these modes. To overcome this limitation, an optimization technique is employed which is capable of placing the first five modes within a 200 kHz bandwidth.},
keywords = {AFM, Cantilever, MEMS, Multifrequency AFM, Piezoelectric Transducers and Drives, Sensors, SPM, System Identification},
pubstate = {published},
tppubtype = {inproceedings}
}

This article presents a novel cantilever design approach to place higher mode frequencies within a specific frequency band to alleviate instrumentation and Q control feasibility. This work is motivated by the emerging field of multifrequency atomic force microscopy (AFM) which involves the excitation and/or detection of several cantilever modes at once. Unlike other operating modes, multifrequency AFM allows the tracking of the sample topography on the fundamental mode while simultaneously acquiring complimentary nanomechanical information on a higher mode. However, higher modes of conventional rectangular tapping-mode cantilevers are usually in the MHz regime and therefore impose severe restrictions on the direct controllability of these modes. To overcome this limitation, an optimization technique is employed which is capable of placing the first five modes within a 200 kHz bandwidth.

This article describes the design, modeling and simulation of a serial-kinematic nanopositioner machined from a single sheet of piezoelectric material. In this class of nanopositioners, the flexures, sensors and actuators are completely integrated into a single monolithic structure. A non-trivial electrode topology is etched into the sheet to achieve in-plane bending and displacement of the moving platform. Finite element analysis predicts a sensitivity of 18.6 nm/V in the x-axis and 18.1 nm/V in the yaxis with a voltage limit of −250V to 1000 V. The first resonance frequency is 250 Hz in the Z axis. This design enables high-speed, long-range, lateral positioning in space-limited applications.

@article{J18f,
title = {A Comparison Of Scanning Methods And The Vertical Control Implications For Scanning Probe Microscopy},
author = {Y. R. Teo and Y. K. Yong and A. J. Fleming},
url = {http://www.precisionmechatronicslab.com/wp-content/uploads/2017/01/J17d.pdf},
doi = {10.1002/asjc.1422},
year = {2018},
date = {2018-07-01},
journal = {Asian Journal of Control},
volume = {30},
number = {4},
pages = {1-15},
abstract = {This article compares the imaging performance of non-traditional scanning patterns for scanning probe microscopy including sinusoidal raster, spiral, and Lissajous patterns. The metrics under consideration include the probe velocity, scanning frequency, and required sampling rate. The probe velocity is investigated in detail as this quantity is proportional to the required bandwidth of the vertical feedback loop and has a major impact on image quality. By considering a sample with an impulsive Fourier transform, the effect of scanning trajectories on imaging quality can be observed and quantified. The non-linear trajectories are found to spread the topography signal bandwidth which has important implications for both low and high-speed imaging. These effects are studied analytically and demonstrated experimentally with a periodic calibration grating. },
keywords = {Scan Pattern, SPM},
pubstate = {published},
tppubtype = {article}
}

This article compares the imaging performance of non-traditional scanning patterns for scanning probe microscopy including sinusoidal raster, spiral, and Lissajous patterns. The metrics under consideration include the probe velocity, scanning frequency, and required sampling rate. The probe velocity is investigated in detail as this quantity is proportional to the required bandwidth of the vertical feedback loop and has a major impact on image quality. By considering a sample with an impulsive Fourier transform, the effect of scanning trajectories on imaging quality can be observed and quantified. The non-linear trajectories are found to spread the topography signal bandwidth which has important implications for both low and high-speed imaging. These effects are studied analytically and demonstrated experimentally with a periodic calibration grating.

A fundamental component of the z-axis feedback loop in amplitude modulation atomic force microscopy is the demodulator. It dictates both bandwidth and noise in the amplitude and phase estimate of the cantilever deflection signal. In this paper, we derive a linear time-invariant model of a closedloop demodulator with user definable tracking bandwidth and sensitivity to other frequency components. A direct demodulator design method is proposed based on the reformulation of the Lyapunov filter as a modulated-demodulated controller in closed loop with a unity plant. Simulation and experimental results for a higher order Lyapunov filter as well as Butterworth and Chebyshev type demodulators are presented.

@article{Ruppert2018b,
title = {Self-sensing, estimation and control in multifrequency Atomic Force Microscopy. },
author = {M. G. Ruppert},
url = {https://royalsoc.org.au/images/pdf/journal/151-1-Ruppert.pdf},
issn = {0035-9173/18/010111-01},
year = {2018},
date = {2018-06-01},
journal = {Journal & Proceedings of the Royal Society of New South Wales},
volume = {151},
number = {1},
pages = {111},
abstract = {Despite the undeniable success of the atomic force microscope (AFM), dynamic techniques still face limitations in terms of spatial resolution, imaging speed and high cost of acquisition. In order to expand the capabilities of the instrument, it was realized that the information about the nano-mechanical properties of a sample are encoded over a range of frequencies and the excitation and detection of higher-order eigenmodes of the micro-cantilever open up further informa-
tion channels. The ability to control these modes and their fast responses to excitation is believed to be the key to unravelling the true potential of these ethods. This work addresses three major drawbacks of the standard AFM setup, which limit the feasibility of multi-frequency approaches.

First, microelectromechanical system (MEMS) probes with integrated piezoelectric layers is motivated, enabling the development of novel multimode self-sensing and self-actuating techniques. Specifically, these piezoelectric transduction schemes permit the miniaturization of the entire AFM towards a cost-effective single-chip device with nanoscale precision in a much smaller form factor than that of conventional macroscale instruments.

Last, in light of the demand for constantly increasing imaging speeds while providing multi-frequency flexibility, the estimation of multiple components of the high-frequency deflection signal is performed with a linear time-varying multi-frequency Kalman filter. The chosen representation allows for an efficient high-bandwidth implementation on a Field Programmable Gate Array. Tracking bandwidth, noise performance and trimodal AFM imaging on a two-component polymer sample are verified and shown to be superior to that of the commonly used lock-in amplifier.},
keywords = {Cantilever, MEMS, Multifrequency AFM, Sensors, Smart Structures, SPM, System Identification, Vibration Control},
pubstate = {published},
tppubtype = {article}
}

Despite the undeniable success of the atomic force microscope (AFM), dynamic techniques still face limitations in terms of spatial resolution, imaging speed and high cost of acquisition. In order to expand the capabilities of the instrument, it was realized that the information about the nano-mechanical properties of a sample are encoded over a range of frequencies and the excitation and detection of higher-order eigenmodes of the micro-cantilever open up further informa-
tion channels. The ability to control these modes and their fast responses to excitation is believed to be the key to unravelling the true potential of these ethods. This work addresses three major drawbacks of the standard AFM setup, which limit the feasibility of multi-frequency approaches.

First, microelectromechanical system (MEMS) probes with integrated piezoelectric layers is motivated, enabling the development of novel multimode self-sensing and self-actuating techniques. Specifically, these piezoelectric transduction schemes permit the miniaturization of the entire AFM towards a cost-effective single-chip device with nanoscale precision in a much smaller form factor than that of conventional macroscale instruments.

Last, in light of the demand for constantly increasing imaging speeds while providing multi-frequency flexibility, the estimation of multiple components of the high-frequency deflection signal is performed with a linear time-varying multi-frequency Kalman filter. The chosen representation allows for an efficient high-bandwidth implementation on a Field Programmable Gate Array. Tracking bandwidth, noise performance and trimodal AFM imaging on a two-component polymer sample are verified and shown to be superior to that of the commonly used lock-in amplifier.

@conference{Ruppert2018,
title = {Advanced Sensing and Control with Active Cantilevers for Multimodal Atomic Force Microscopy},
author = {M. G. Ruppert and S. I. Moore and M. Zawierta and G. Putrino and Y. K. Yong},
year = {2018},
date = {2018-04-18},
booktitle = {7th Multifrequency AFM Conference},
address = {Madrid, Spain},
abstract = {Atomic force microscopy (AFM) cantilevers with integrated actuation and sensing on the chip level provide several distinct advantages over conventional cantilever instrumentation. These include clean frequency responses, the possibility of down-scaling and parallelization to cantilever arrays as well as the absence of optical interferences. While cantilever microfabrication technology has continuously advanced over the years, the overall design has remained largely unchanged; a passive rectangular shaped cantilever design has been adopted as the industry wide standard. Consequently, conventional cantilever instrumentation requires external piezo acoustic excitation as well as an external optical deflection sensor. Both of these components are not optimal for current trends in multifrequency AFM technology which revolve around further down-sizing, parallelization and measurements at multiple higher eigenmodes. Using microelectromechanical systems (MEMS) fabrication processes, this work aims to optimize cantilever instrumentation by realizing a new class of probes with high-performance integrated actuators and sensors. Equipped with multiple integrated piezoelectric layers for both actuation and sensing, these cantilevers are capable of achieving an increased higher eigenmode sensitivity and/or guaranteed collocated system properties compared to commercially available counterparts; examples of such designs are shown in Figure 1. The geometry as well as the integrated actuator/sensor arrangement is optimized using finite element modelling with individual design goals. The designs are realized using a commercial MEMS fabrication process and only require a simple five-mask patterning and etching process and post-fabricated sharp tips.},
keywords = {AFM, Cantilever, MEMS, Multifrequency AFM, Sensors, Smart Structures, SPM, Vibration Control},
pubstate = {published},
tppubtype = {conference}
}

Atomic force microscopy (AFM) cantilevers with integrated actuation and sensing on the chip level provide several distinct advantages over conventional cantilever instrumentation. These include clean frequency responses, the possibility of down-scaling and parallelization to cantilever arrays as well as the absence of optical interferences. While cantilever microfabrication technology has continuously advanced over the years, the overall design has remained largely unchanged; a passive rectangular shaped cantilever design has been adopted as the industry wide standard. Consequently, conventional cantilever instrumentation requires external piezo acoustic excitation as well as an external optical deflection sensor. Both of these components are not optimal for current trends in multifrequency AFM technology which revolve around further down-sizing, parallelization and measurements at multiple higher eigenmodes. Using microelectromechanical systems (MEMS) fabrication processes, this work aims to optimize cantilever instrumentation by realizing a new class of probes with high-performance integrated actuators and sensors. Equipped with multiple integrated piezoelectric layers for both actuation and sensing, these cantilevers are capable of achieving an increased higher eigenmode sensitivity and/or guaranteed collocated system properties compared to commercially available counterparts; examples of such designs are shown in Figure 1. The geometry as well as the integrated actuator/sensor arrangement is optimized using finite element modelling with individual design goals. The designs are realized using a commercial MEMS fabrication process and only require a simple five-mask patterning and etching process and post-fabricated sharp tips.

In this review paper, traditional and novel demodulation methods applicable to amplitude modulation atomic force microscopy are implemented on a widely used digital processing system. As a crucial bandwidth-limiting component in the z-axis feedback loop of an atomic force microscope, the purpose of the demodulator is to obtain estimates of amplitude and phase of the cantilever deflection signal in the presence of sensor noise or additional distinct frequency components. Specifically for modern multifrequency techniques, where higher harmonic and/or higher eigenmode contributions are present in the oscillation signal, the fidelity of the estimates obtained from some demodulation techniques is not guaranteed. To enable a rigorous comparison, the performance metrics tracking bandwidth, implementation complexity and sensitivity to other frequency components are experimentally evaluated for each method. Finally, the significance of an adequate demodulator bandwidth is highlighted during high-speed tapping-mode AFM experiments in constant height mode.

@article{J17e,
title = {Lyapunov Estimator for High-Speed Demodulation in Dynamic Mode Atomic Force Microscopy},
author = {M. R. P. Ragazzon and M. G. Ruppert and D. M. Harcombe and A. J. Fleming and J. T. Gravdahl},
url = {http://www.precisionmechatronicslab.com/wp-content/uploads/2017/09/J17e.pdf},
year = {2017},
date = {2017-08-01},
journal = {IEEE Transactions on Control Systems Technology},
volume = {26},
number = {2},
pages = {765-772},
abstract = {In dynamic mode atomic force microscopy (AFM), the imaging bandwidth is governed by the slowest component in the open-loop chain consisting of the vertical actuator, cantilever and demodulator. While the common demodulation method is to use a lock-in amplifier (LIA), its performance is ultimately bounded by the bandwidth of the post-mixing low-pass filters. This article proposes an amplitude and phase estimation method based on a strictly positive real Lyapunov design approach. The estimator is designed to be of low complexity while allowing for high bandwidth. Additionally, suitable gains for high performance are suggested such that no tuning is necessary. The Lyapunov estimator is experimentally implemented for amplitude demodulation and shown to surpass the LIA in terms of tracking bandwidth and noise performance. High-speed AFM images are presented to corroborate the results.},
keywords = {AFM, SPM},
pubstate = {published},
tppubtype = {article}
}

In dynamic mode atomic force microscopy (AFM), the imaging bandwidth is governed by the slowest component in the open-loop chain consisting of the vertical actuator, cantilever and demodulator. While the common demodulation method is to use a lock-in amplifier (LIA), its performance is ultimately bounded by the bandwidth of the post-mixing low-pass filters. This article proposes an amplitude and phase estimation method based on a strictly positive real Lyapunov design approach. The estimator is designed to be of low complexity while allowing for high bandwidth. Additionally, suitable gains for high performance are suggested such that no tuning is necessary. The Lyapunov estimator is experimentally implemented for amplitude demodulation and shown to surpass the LIA in terms of tracking bandwidth and noise performance. High-speed AFM images are presented to corroborate the results.

@inproceedings{C17e,
title = {Higher-harmonic AFM Imaging with a High-Bandwidth Multifrequency Lyapunov Filter},
author = {D. M. Harcombe and M. G. Ruppert and A. J. Fleming},
year = {2017},
date = {2017-07-03},
booktitle = {IEEE/ASME Advanced Intelligent Mechatronics (AIM)},
address = {Munich, Germany},
abstract = {A major difficulty in multifrequency atomic force microscopy (MF-AFM) is the accurate estimation of amplitude and phase at multiple frequencies for both z-axis feedback and material contrast imaging. Typically a lock-in amplifier is chosen as it is both narrowband and simple to implement. However, it inherently suffers drawbacks including a limited bandwidth due to post mixing low-pass filters and the necessity for multiple to be operated in parallel for MF-AFM. This paper proposes a multifrequency demodulator in the form of a modelbased Lyapunov filter implemented on a Field Programmable Gate Array (FPGA). System modelling and simulations are verified by experimental results demonstrating high tracking bandwidth and off-mode rejection at modelled frequencies. Additionally, AFM scans with a five-frequency-based system are presented wherein higher harmonic imaging is performed up to 1 MHz.},
keywords = {Multifrequency AFM, SPM},
pubstate = {published},
tppubtype = {inproceedings}
}

A major difficulty in multifrequency atomic force microscopy (MF-AFM) is the accurate estimation of amplitude and phase at multiple frequencies for both z-axis feedback and material contrast imaging. Typically a lock-in amplifier is chosen as it is both narrowband and simple to implement. However, it inherently suffers drawbacks including a limited bandwidth due to post mixing low-pass filters and the necessity for multiple to be operated in parallel for MF-AFM. This paper proposes a multifrequency demodulator in the form of a modelbased Lyapunov filter implemented on a Field Programmable Gate Array (FPGA). System modelling and simulations are verified by experimental results demonstrating high tracking bandwidth and off-mode rejection at modelled frequencies. Additionally, AFM scans with a five-frequency-based system are presented wherein higher harmonic imaging is performed up to 1 MHz.

@inproceedings{Moore2017b,
title = {Design and Analysis of Piezoelectric Cantilevers with Enhanced Higher Eigenmodes for Atomic Force Microscopy},
author = {S. I. Moore and M. G. Ruppert and Y. K. Yong},
year = {2017},
date = {2017-07-02},
booktitle = {IEEE/ASME Advanced Intelligent Mechatronics (AIM)},
address = {Munich, Germany},
abstract = {Atomic force microscope (AFM) cantilevers with
integrated actuation and sensing provide several distinct advantages
over conventional cantilever instrumentation such as
clean frequency responses, the possibility of down-scaling and
parallelization to cantilever arrays as well as the absence of optical
interferences. However, for multifrequency AFM techniques
involving higher eigenmodes of the cantilever, optimization
of the transducer location and layout has to be taken into
account. This work proposes multiple integrated piezoelectric
regions on the cantilever which maximize the deflection of the
cantilever and the piezoelectric charge response for a given
higher eigenmode based on the spatial strain distribution. Finite
element analysis is performed to find the optimal transducer
topology and experimental results are presented which highlight
an actuation gain improvement up to 42 dB on the third mode
and sensor sensitivity improvement up to 38 dB on the second
mode.},
keywords = {Multifrequency AFM, SPM},
pubstate = {published},
tppubtype = {inproceedings}
}

Atomic force microscope (AFM) cantilevers with
integrated actuation and sensing provide several distinct advantages
over conventional cantilever instrumentation such as
clean frequency responses, the possibility of down-scaling and
parallelization to cantilever arrays as well as the absence of optical
interferences. However, for multifrequency AFM techniques
involving higher eigenmodes of the cantilever, optimization
of the transducer location and layout has to be taken into
account. This work proposes multiple integrated piezoelectric
regions on the cantilever which maximize the deflection of the
cantilever and the piezoelectric charge response for a given
higher eigenmode based on the spatial strain distribution. Finite
element analysis is performed to find the optimal transducer
topology and experimental results are presented which highlight
an actuation gain improvement up to 42 dB on the third mode
and sensor sensitivity improvement up to 38 dB on the second
mode.

A fundamental but often overlooked component in the z-axis feedback loop of the atomic force microscope (AFM) operated in dynamic mode is the demodulator. It’s purpose is to obtain a preferably fast and low-noise estimate of amplitude and phase of the cantilever deflection signal in the presence of sensor noise and additional distinct frequency components. In this paper, we implement both traditional and recently developed robust methods on a labVIEW digital processing system and rigorously compare these techniques experimentally in terms of measurement bandwidth, implementation complexity and robustness to noise. We conclude with showing high-speed tapping-mode AFM images in constant height, highlighting the significance of an adequate demodulator bandwidth.

This paper presents a novel microelectromechanical
systems (MEMS) implementation of an on-chip atomic
force microscope (AFM), fabricated using a silicon-on-insulator
process. The device features an XY scanner with electrostatic
actuators and electrothermal sensors, as well as an integrated
silicon microcantilever. A single AlN piezoelectric electrode is
used for simultaneous actuation and deflection sensing of the
cantilever via a charge sensing technique. With the device being
operated in closed loop, the probe scanner is successfully used to
obtain 8mmx8mm tapping-mode AFM images of a calibration
grating.

@article{Moore2017,
title = {Design and Characterization of Cantilevers for Multi-Frequency Atomic Force Microscopy},
author = {S. I. Moore and Y. K. Yong},
url = {http://www.precisionmechatronicslab.com/wp-content/uploads/2017/01/MNL.2016.0586.pdf},
doi = {10.1049/mnl.2016.0586},
year = {2017},
date = {2017-03-01},
journal = {Micro & Nano Letters},
volume = {12},
number = {5},
pages = {315-320},
abstract = {The experimental characterisation of a set of microcantilevers targeted at use in multi-frequency atomic force microscope is presented. The aim of this work is to design a cantilever that naturally amplifies its harmonic oscillations which are introduced by nonlinear probe–sample
interaction forces. This is performed by placing the modal frequencies of the cantilever at integer multiples of the first modal frequency. The developed routine demonstrates the placement of the frequency of the second to fifth mode. The characterisation shows a trend that
lower-order modes are more accurately placed than higher-order modes. With two fabricated designs, the error in the second mode is at most 2.26% while the greatest error in the fifth mode is at 10.5%.},
keywords = {Cantilever, MEMS, Multifrequency AFM, SPM},
pubstate = {published},
tppubtype = {article}
}

The experimental characterisation of a set of microcantilevers targeted at use in multi-frequency atomic force microscope is presented. The aim of this work is to design a cantilever that naturally amplifies its harmonic oscillations which are introduced by nonlinear probe–sample
interaction forces. This is performed by placing the modal frequencies of the cantilever at integer multiples of the first modal frequency. The developed routine demonstrates the placement of the frequency of the second to fifth mode. The characterisation shows a trend that
lower-order modes are more accurately placed than higher-order modes. With two fabricated designs, the error in the second mode is at most 2.26% while the greatest error in the fifth mode is at 10.5%.

@article{Moore2017b,
title = {Multimodal cantilevers with novel piezoelectric layer topology for sensitivity enhancement},
author = {S. I. Moore and M. G. Ruppert and Y. K. Yong},
url = {http://www.precisionmechatronicslab.com/wp-content/uploads/2017/02/2190-4286-8-38.pdf},
year = {2017},
date = {2017-02-06},
journal = {Beilstein Journal of Nanotechnology},
volume = {8},
pages = {358--371},
abstract = {Self-sensing techniques for atomic force microscope (AFM) cantilevers have several advantageous characteristics compared to the optical beam deflection method. The possibility of down scaling, parallelization of cantilever arrays and the absence of optical interference associated imaging artifacts have led to an increased research interest in these methods. However, for multifrequency AFM, the optimization of the transducer layout on the cantilever for higher order modes has not been addressed. To fully utilize an integrated piezoelectric transducer, this work alters the layout of the piezoelectric layer to maximize both the deflection of the cantilever and measured piezoelectric charge response for a given mode with respect to the spatial distribution of the strain. On a prototype cantilever design, significant increases in actuator and sensor sensitivities were achieved for the first four modes without any substantial increase in sensor noise. The transduction mechanism is specifically targeted at multifrequency AFM and has the potential to provide higher resolution imaging on higher order modes.},
keywords = {Cantilever, Multifrequency AFM, Piezoelectric Transducers and Drives, SPM},
pubstate = {published},
tppubtype = {article}
}

Self-sensing techniques for atomic force microscope (AFM) cantilevers have several advantageous characteristics compared to the optical beam deflection method. The possibility of down scaling, parallelization of cantilever arrays and the absence of optical interference associated imaging artifacts have led to an increased research interest in these methods. However, for multifrequency AFM, the optimization of the transducer layout on the cantilever for higher order modes has not been addressed. To fully utilize an integrated piezoelectric transducer, this work alters the layout of the piezoelectric layer to maximize both the deflection of the cantilever and measured piezoelectric charge response for a given mode with respect to the spatial distribution of the strain. On a prototype cantilever design, significant increases in actuator and sensor sensitivities were achieved for the first four modes without any substantial increase in sensor noise. The transduction mechanism is specifically targeted at multifrequency AFM and has the potential to provide higher resolution imaging on higher order modes.

We report on the application of internal model control for accurate tracking of a spiral trajectory for atomic force microscopy (AFM). With a closed-loop bandwidth of only 300 Hz, we achieved tracking errors as low as 0.31% of the scan diameter and an ultravideo frame rate for a high pitch (30 nm) spiral trajectory generated by amplitude modulation of 3 kHz sinusoids. Design and synthesis procedures are proposed for a smooth modulating waveform to minimize the steady-state tracking error during sequential imaging. To obtain AFM images under the constant force condition, a high bandwidth analogue proportional integral controller is applied to the damped z-axis of a flexure nanopositioner. Efficacy of the proposed method was demonstrated by artifact-free images at a rate of 37.5 frames/s.

The atomic force microscope (AFM) is an invaluable scientific tool; however, its conventional implementation as a relatively costly macroscale system is a barrier to its more widespread use. A microelectromechanical systems (MEMS) approach to AFM design has the potential to significantly reduce the cost and complexity of the AFM, expanding its utility beyond current applications. This paper presents an on-chip AFM based on a silicon-on-insulator MEMS fabrication process. The device features integrated xy electrostatic actuators and electrothermal sensors as well as an AlN piezoelectric layer for out-of-plane actuation and integrated deflection sensing of a microcantilever. The three-degree-of-freedom design allows the probe scanner to obtain topographic tapping-mode AFM images with an imaging range of up to 8μm x 8μm in closed loop.

@article{J16d,
title = {High-speed Vertical Positioning Stage with Integrated Dual-sensor Arrangement},
author = {Y. K. Yong and A. J. Fleming},
url = {http://www.precisionmechatronicslab.com/wp-content/uploads/2016/08/1-s2.0-S0924424716303302-main-1.pdf},
year = {2016},
date = {2016-12-01},
journal = {Sensors & Actuators: A. Physical},
volume = {248},
pages = {184--192},
abstract = {This article presents a novel vertical positioning stage with a dual-sensor arrangement suitable for scanning probe microscopy. The stage has a travel range of 8.4um and a first resonance frequency of 24kHz in the direction of travel. The sensor arrangement consists of an integrated piezoelectric force sensor and laminated piezoresistive strain sensor. The piezoelectric force sensor exhibits extremely low noise and introduces a zero into the dynamics which allows the use of integral force feedback. This control method provides excellent damping performance and guaranteed stability. The piezoresistive sensor is used for tracking control with an analog PI controller which is shown to be an approximate inverse of the damped system. The resulting closed-loop system has a bandwidth is 11.4kHz and 6-sigma resolution of 3.6nm, which is ideal for nanopositioning and atomic force microscopy (AFM) applications. The proposed vertical stage is used to replace the vertical axis of a commercial AFM. Scans are performed in constant-force contact mode with a tip velocity of 0.2mm/s, 1mm/s and 2mm/s. The recorded images contain negligible artefacts due to insufficient vertical bandwidth.},
keywords = {Nanopositioning, Optics, SPM},
pubstate = {published},
tppubtype = {article}
}

This article presents a novel vertical positioning stage with a dual-sensor arrangement suitable for scanning probe microscopy. The stage has a travel range of 8.4um and a first resonance frequency of 24kHz in the direction of travel. The sensor arrangement consists of an integrated piezoelectric force sensor and laminated piezoresistive strain sensor. The piezoelectric force sensor exhibits extremely low noise and introduces a zero into the dynamics which allows the use of integral force feedback. This control method provides excellent damping performance and guaranteed stability. The piezoresistive sensor is used for tracking control with an analog PI controller which is shown to be an approximate inverse of the damped system. The resulting closed-loop system has a bandwidth is 11.4kHz and 6-sigma resolution of 3.6nm, which is ideal for nanopositioning and atomic force microscopy (AFM) applications. The proposed vertical stage is used to replace the vertical axis of a commercial AFM. Scans are performed in constant-force contact mode with a tip velocity of 0.2mm/s, 1mm/s and 2mm/s. The recorded images contain negligible artefacts due to insufficient vertical bandwidth.

Emerging multifrequency atomic force microscopy (MF-AFM) methods rely on coherent demodulation of the cantilever deflection signal at multiple frequencies. These measurements are needed in order to close the z-axis feedback loop and to acquire complementary information on the tip-sample interaction. While the common method is to use a lock-in amplifier capable of recovering low-level signals from noisy backgrounds, its performance is ultimately bounded by the bandwidth of the low-pass filters. In light of the demand for constantly increasing imaging speeds while providing multifrequency flexibility, we propose to estimate the in-phase and quadrature components with a linear time-varying Kalman filter. The chosen representation allows for an efficient high-bandwidth implementation on a Field Programmable Gate Array (FPGA). Tracking bandwidth and noise performance are verified experimentally and trimodal AFM results on a two-component polymer sample highlight the applicability of the proposed method for MF-AFM.

@inproceedings{C16g,
title = {Iterative Control for Periodic Tasks with Robustness Considerations, Applied to a Nanopositioning Stage},
author = {R. de Rozario and A. J. Fleming and T. Oomen},
year = {2016},
date = {2016-09-05},
booktitle = {IFAC Symposium on Mechatronic Systems},
address = {Loughborough, UK},
abstract = {Nanopositioning stages are an example of motion systems that are required to accurately perform a high frequent repetitive scanning motion. The tracking performance can be signicantly increased by iteratively updating a feedforward input by using a nonparametric inverse plant model. However, in this paper it is shown that current approaches lack systematic robustness considerations and are suering from limited design freedom to enforce satisfying convergence behavior. Therefore, inspired by existing the Iterative Learning Control approach, robustness is added to the existing methods to enable the desired convergence behavior. This results in the Robust Iterative Inversion-based Control method, whose potential for superior convergence is experimentally veried on a Nanopositioning system.},
keywords = {Nanopositioning, SPM},
pubstate = {published},
tppubtype = {inproceedings}
}

Nanopositioning stages are an example of motion systems that are required to accurately perform a high frequent repetitive scanning motion. The tracking performance can be signicantly increased by iteratively updating a feedforward input by using a nonparametric inverse plant model. However, in this paper it is shown that current approaches lack systematic robustness considerations and are suering from limited design freedom to enforce satisfying convergence behavior. Therefore, inspired by existing the Iterative Learning Control approach, robustness is added to the existing methods to enable the desired convergence behavior. This results in the Robust Iterative Inversion-based Control method, whose potential for superior convergence is experimentally veried on a Nanopositioning system.

@inproceedings{C16e,
title = {Design, Modeling, and Characterization of an XY Nanopositioning Stage Constructed from a Single Sheet of Piezoelectric Material},
author = {A. J. Fleming and G. Berriman and Y. K. Yong},
year = {2016},
date = {2016-07-12},
booktitle = {IEEE Advanced Intelligent Mechatronics},
address = {Banff, Canada},
abstract = {This article describes the design, fabrication and testing of a new XY nanopositioning stage constructed from a single sheet of piezoelectric material. The approach involves direct ultrasonic machining of a piezoelectric sheet to create flexural and actuator features. An industrial inkjet printer is then used to create electrode features by printing Nitric Acid directly onto the evaporated metal surface of the piezo sheet. The result is a monolithic piezoelectric structure with individual electrical control over each actuator feature. Experimental results demonstrate a full-scale range of 9um in the X and Y axes, and a first resonance frequency of 230Hz in the Z axes. The completed nanopositioner is the thinnest yet reported with a thickness of only 500um. The new design method will enable a new range of ultra-compact applications in scanning probe microscopy, scanning electron microscopy, and active optics. },
keywords = {Nanopositioning, SPM},
pubstate = {published},
tppubtype = {inproceedings}
}

This article describes the design, fabrication and testing of a new XY nanopositioning stage constructed from a single sheet of piezoelectric material. The approach involves direct ultrasonic machining of a piezoelectric sheet to create flexural and actuator features. An industrial inkjet printer is then used to create electrode features by printing Nitric Acid directly onto the evaporated metal surface of the piezo sheet. The result is a monolithic piezoelectric structure with individual electrical control over each actuator feature. Experimental results demonstrate a full-scale range of 9um in the X and Y axes, and a first resonance frequency of 230Hz in the Z axes. The completed nanopositioner is the thinnest yet reported with a thickness of only 500um. The new design method will enable a new range of ultra-compact applications in scanning probe microscopy, scanning electron microscopy, and active optics.

A homodyne path stabilised Michelson based interferometer displacement sensor was developed. This sensor achieved a noise floor of 100 fm/rt(Hz), for frequencies higher than 100 kHz. A prototype AFM that integrated this sensor was developed. Using tapping mode, topography maps of an AFM test grid were produced.

A fundamental component in the z-axis feedback loop of an atomic force microscope (AFM) operated in dynamic mode is the lock-in amplifier to obtain amplitude and phase of the high-frequency cantilever deflection signal. While this narrowband demodulation technique is capable of filtering noise far away from the carrier and modulation frequency, its performance is ultimately bounded by the bandwidth of its low-pass filter which is employed to suppress the frequency component at twice the carrier frequency. Moreover, multiple eigenmodes and higher harmonics are used for imaging in modern multifrequency AFMs, which necessitates multiple lock-in amplifiers to recover the respective amplitude and phase information. We propose to estimate amplitude and phase of multiple frequency components with a linear time-varying Kalman filter which allows for an efficient implementation on a Field Programmable Gate Array (FPGA). While experimental results for the single mode case have already proven to increase the imaging bandwidth in tapping-mode AFM, multifrequency simulations promise further improvement in imaging flexibility.

@article{Ruppert2016b,
title = {Multimode Q Control in Tapping-Mode AFM: Enabling Imaging on Higher Flexural Eigenmodes},
author = {M. G. Ruppert and S. O. R. Moheimani},
doi = {10.1109/TCST.2015.2478077},
year = {2016},
date = {2016-07-01},
journal = {IEEE Transactions on Control Systems Technology},
volume = {24},
number = {4},
pages = {1149-1159},
abstract = {Numerous dynamic Atomic Force Microscopy (AFM) methods have appeared in recent years, which make use of the excitation and detection of higher order eigenmodes of the microcantilever. The ability to control these modes and their responses to excitation is believed to be the key to unraveling the true potential of these methods. In this work, we highlight a multi-mode Q control method that exhibits remarkable damping performance and stability robustness. The experimental results obtained in ambient conditions demonstrate improved imaging stability by damping non-driven resonant modes when scanning is performed at a higher eigenmode of the cantilever. Higher scan speeds are shown to result from a decrease in transient response time. },
keywords = {MEMS, Multifrequency AFM, SPM, System Identification, Vibration Control},
pubstate = {published},
tppubtype = {article}
}

Numerous dynamic Atomic Force Microscopy (AFM) methods have appeared in recent years, which make use of the excitation and detection of higher order eigenmodes of the microcantilever. The ability to control these modes and their responses to excitation is believed to be the key to unraveling the true potential of these methods. In this work, we highlight a multi-mode Q control method that exhibits remarkable damping performance and stability robustness. The experimental results obtained in ambient conditions demonstrate improved imaging stability by damping non-driven resonant modes when scanning is performed at a higher eigenmode of the cantilever. Higher scan speeds are shown to result from a decrease in transient response time.

A fundamental challenge in dynamic mode atomic force microscopy (AFM) is the estimation of the cantilever oscillation amplitude from the deflection signal which might be distorted by noise and/or high-frequency components. When the cantilever is excited at resonance, its deflection is typically obtained via narrowband demodulation using a lock-in amplifier. However, the bandwidth of this measurement technique is ultimately bounded by the low-pass filter which must be employed after demodulation to attenuate the component at twice the carrier frequency. Furthermore, to measure the amplitude of multiple frequency components such as higher eigenmodes and/or higher harmonics in multifrequency AFM, multiple lock-in amplifiers must be employed. In this work, the authors propose the estimation of amplitude and phase using a linear time-varying Kalman filter which is easily extended to multiple frequencies. Experimental results are obtained using square-modulated sine waves and closed-loop AFM scans, verifying the performance of the proposed Kalman filter.

This article describes an improvement to integral resonance damping control (IRC) for reference tracking applications such as Scanning Probe Microscopy and nanofabrication. It is demonstrated that IRC control introduces a low-frequency pole into the tracking loop which is detrimental for performance. In this work, the location of this pole is found analytically using Cardano’s method then compensated by parameterizing the tracking controller accordingly. This approach maximizes the closed-loop bandwidth whilst being robust to changes in the resonance frequencies. The refined IRC controller is comprehensively compared to other low-order methods in a practical environment.

@inproceedings{Maroufi2015,
title = {Design and Control of a MEMS Nanopositioner with Bulk Piezoresistive Sensors},
author = {M. Maroufi and Y. K. Yong and S. O. R. Moheimani },
url = {http://www.eng.newcastle.edu.au/~yy582/Papers/Maroufi2015.pdf},
year = {2015},
date = {2015-09-01},
booktitle = {IEEE Multiconference on Systems and Control, Sydney, Australia},
abstract = {A 2 degree of freedom microelectromechanical system (MEMS) nanopositioner is presented in this paper. The nanopositioner is fabricated using a standard silicon-on-insulator process. The device demonstrates a bidirectional displacement in two orthogonal directions. As the displacement sensing mechanism, bulk piezoresistivity of tilted clamped-guided beams is exploited. The characterization reveals more than 15 μm displacement range and an in-plane bandwidth of above 3.6 kHz in both axes. The piezoresistive sensors provide a bandwidth which is more than ten times larger than the stage's resonant frequency. To evaluate the sensor performance in closed-loop, an integral resonant controller together with an integral tracking controller are implemented where piezoresistive sensor outputs are used as measurement. The controlled nanopositioner is used for imaging in an atomic force microscope.},
keywords = {MEMS, Nanopositioning, Sensors, SPM},
pubstate = {published},
tppubtype = {inproceedings}
}

A 2 degree of freedom microelectromechanical system (MEMS) nanopositioner is presented in this paper. The nanopositioner is fabricated using a standard silicon-on-insulator process. The device demonstrates a bidirectional displacement in two orthogonal directions. As the displacement sensing mechanism, bulk piezoresistivity of tilted clamped-guided beams is exploited. The characterization reveals more than 15 μm displacement range and an in-plane bandwidth of above 3.6 kHz in both axes. The piezoresistive sensors provide a bandwidth which is more than ten times larger than the stage's resonant frequency. To evaluate the sensor performance in closed-loop, an integral resonant controller together with an integral tracking controller are implemented where piezoresistive sensor outputs are used as measurement. The controlled nanopositioner is used for imaging in an atomic force microscope.

@inproceedings{Ruppert2015,
title = {Multi-Mode Q Control in Multifrequency Atomic Force Microscopy},
author = {M. G. Ruppert and S. O. R. Moheimani},
doi = {10.1115/DETC2015-46989},
year = {2015},
date = {2015-08-01},
booktitle = {ASME International Design Engineering Technical Conferences & Computers and Information in Engineering Conference},
pages = {V004T09A009},
address = {Boston, Massachusetts, USA},
abstract = {Various Atomic Force Microscopy (AFM) modes have emerged which rely on the excitation and detection of multiple eigenmodes of the microcantilever. The conventional control loops employed in multifrequency AFM (MF-AFM) such as bimodal imaging where the fundamental mode is used to map the topography and a higher eigenmode is used to map sample material properties only focus on maintaining low bandwidth signals such as amplitude and/ or frequency shift. However, the ability to perform additional high bandwidth control of the quality (Q) factor of the participating modes is believed to be imperative to unfolding the full potential of these methods. This can be achieved by employing a multi-mode Q control approach utilizing positive position feedback. The controller exhibits remarkable performance in arbitrarily modifying the Q factor of multiple eigenmodes as well as guaranteed stability properties when used on flexible structures with collocated actuators and sensors. A controller design method based on pole placement optimization is proposed for setting an arbitrary on-resonance Q factor of the participating eigenmodes. Experimental results using bimodal AFM imaging on a two component polymer sample are presented.},
keywords = {MEMS, Multifrequency AFM, SPM, Vibration Control},
pubstate = {published},
tppubtype = {inproceedings}
}

Various Atomic Force Microscopy (AFM) modes have emerged which rely on the excitation and detection of multiple eigenmodes of the microcantilever. The conventional control loops employed in multifrequency AFM (MF-AFM) such as bimodal imaging where the fundamental mode is used to map the topography and a higher eigenmode is used to map sample material properties only focus on maintaining low bandwidth signals such as amplitude and/ or frequency shift. However, the ability to perform additional high bandwidth control of the quality (Q) factor of the participating modes is believed to be imperative to unfolding the full potential of these methods. This can be achieved by employing a multi-mode Q control approach utilizing positive position feedback. The controller exhibits remarkable performance in arbitrarily modifying the Q factor of multiple eigenmodes as well as guaranteed stability properties when used on flexible structures with collocated actuators and sensors. A controller design method based on pole placement optimization is proposed for setting an arbitrary on-resonance Q factor of the participating eigenmodes. Experimental results using bimodal AFM imaging on a two component polymer sample are presented.

A key hurdle to achieve video-rate atomic force microscopy (AFM) in constant-force contact mode is the inadequate bandwidth of the vertical feedback control loop. This paper describes techniques used to increase the vertical tracking bandwidth of a nanopositioner to a level that is sufficient for video-rate AFM. These techniques involve the combination of: a high-speed XYZ nanopositioner; a passive damping technique that cancels the inertial forces of the Z actuator which in turns eliminates the low 20-kHz vertical resonant mode of the nanopositioner; an active control technique that is used to augment damping to high vertical resonant modes at 60 kHz and above. The implementation of these techniques allows a tenfold increase in the vertical tracking bandwidth, from 2.3 (without damping) to 28.1 kHz. This allows high-quality, video-rate AFM images to be captured at 10 frames/s without noticeable artifacts associated with vibrations and insufficient vertical tracking bandwidth.

2014

@book{B14,
title = {Design, Modeling and Control of Nanopositioning Systems},
author = {A. J. Fleming and K. K. Leang},
url = {http://www.amazon.com/Modeling-Control-Nanopositioning-Advances-Industrial/dp/3319066161 },
isbn = {978-3319066165},
year = {2014},
date = {2014-12-30},
publisher = {Springer},
address = {London, UK},
abstract = {Covering the complete design cycle of nanopositioning systems, this is the first comprehensive text on the topic. The book first introduces concepts associated with nanopositioning stages and outlines their application in such tasks as scanning probe microscopy, nanofabrication, data storage, cell surgery and precision optics. Piezoelectric transducers, employed ubiquitously in nanopositioning applications are then discussed in detail including practical considerations and constraints on transducer response. The reader is then given an overview of the types of nanopositioner before the text turns to the in-depth coverage of mechanical design including flexures, materials, manufacturing techniques, and electronics. This process is illustrated by the example of a high-speed serial-kinematic nanopositioner. Position sensors are then catalogued and described and the text then focuses on control.

Several forms of control are treated: shunt control, feedback control, force feedback control and feedforward control (including an appreciation of iterative learning control). Performance issues are given importance as are problems limiting that performance such as hysteresis and noise which arise in the treatment of control and are then given chapter-length attention in their own right. The reader also learns about cost functions and other issues involved in command shaping, charge drives and electrical considerations. All concepts are demonstrated experimentally including by direct application to atomic force microscope imaging.

Design, Modeling and Control of Nanopositioning Systems will be of interest to researchers in mechatronics generally and in control applied to atomic force microscopy and other nanopositioning applications. Microscope developers and mechanical designers of nanopositioning devices will find the text essential reading.},
keywords = {Nanopositioning, SPM},
pubstate = {published},
tppubtype = {book}
}

Covering the complete design cycle of nanopositioning systems, this is the first comprehensive text on the topic. The book first introduces concepts associated with nanopositioning stages and outlines their application in such tasks as scanning probe microscopy, nanofabrication, data storage, cell surgery and precision optics. Piezoelectric transducers, employed ubiquitously in nanopositioning applications are then discussed in detail including practical considerations and constraints on transducer response. The reader is then given an overview of the types of nanopositioner before the text turns to the in-depth coverage of mechanical design including flexures, materials, manufacturing techniques, and electronics. This process is illustrated by the example of a high-speed serial-kinematic nanopositioner. Position sensors are then catalogued and described and the text then focuses on control.

Several forms of control are treated: shunt control, feedback control, force feedback control and feedforward control (including an appreciation of iterative learning control). Performance issues are given importance as are problems limiting that performance such as hysteresis and noise which arise in the treatment of control and are then given chapter-length attention in their own right. The reader also learns about cost functions and other issues involved in command shaping, charge drives and electrical considerations. All concepts are demonstrated experimentally including by direct application to atomic force microscope imaging.

Design, Modeling and Control of Nanopositioning Systems will be of interest to researchers in mechatronics generally and in control applied to atomic force microscopy and other nanopositioning applications. Microscope developers and mechanical designers of nanopositioning devices will find the text essential reading.

We present new insights into the modeling of the microcantilever in dynamic mode atomic force microscopy and outline a novel high-bandwidth tip-sample force estimation technique for the development of high-bandwidth z-axis control. Fundamental to the proposed technique is the assumption that in tapping mode atomic force microscopy, the tip-sample force takes the form of an impulse train. Formulating the estimation problem as a Kalman filter, the tip-sample force is estimated directly; thus, potentially enabling high-bandwidth z-axis control by eliminating the dependence of the control technique on microcantilever dynamics and the amplitude demodulation technique. Application of this technique requires accurate knowledge of the models of the microcantilever; a novel identification method is proposed. Experimental data are used in an offline analysis for verification.

@inproceedings{Ruppert2014,
title = {Novel Reciprocal Self-Sensing Techniques for Tapping-Mode Atomic Force Microscopy},
author = {M. G. Ruppert and S. O. R. Moheimani},
doi = {https://doi.org/10.3182/20140824-6-ZA-1003.00376},
year = {2014},
date = {2014-08-24},
booktitle = {19th IFAC World Congress},
address = {Cape Town, South Africa},
abstract = {We evaluate two novel reciprocal self-sensing methods for tapping-mode atomic
force microscopy (TM-AFM) utilizing charge measurement and charge actuation, respectively.
A microcantilever, which can be batch fabricated through a standard microelectromechanical
system (MEMS) process, is coated with a single piezoelectric layer and simultaneously used for
actuation and deflection sensing. The setup enables the elimination of the optical beam deflection
technique which is commonly used to measure the cantilever oscillation amplitude. The voltage
to charge and charge to voltage transfer functions reveal a high amount of capacitive feedthrough
which degrades the dynamic range of the sensors significantly. A feedforward control technique
is employed to cancel the feedthrough and increase the dynamic range from less than 1 dB
to approximately 30 dB. Experiments show that the conditioned self-sensing schemes achieve
an excellent signal-to-noise ratio and can therefore be used to provide the feedback signal for
TM-AFM imaging.},
keywords = {MEMS, Smart Structures, SPM},
pubstate = {published},
tppubtype = {inproceedings}
}

We evaluate two novel reciprocal self-sensing methods for tapping-mode atomic
force microscopy (TM-AFM) utilizing charge measurement and charge actuation, respectively.
A microcantilever, which can be batch fabricated through a standard microelectromechanical
system (MEMS) process, is coated with a single piezoelectric layer and simultaneously used for
actuation and deflection sensing. The setup enables the elimination of the optical beam deflection
technique which is commonly used to measure the cantilever oscillation amplitude. The voltage
to charge and charge to voltage transfer functions reveal a high amount of capacitive feedthrough
which degrades the dynamic range of the sensors significantly. A feedforward control technique
is employed to cancel the feedthrough and increase the dynamic range from less than 1 dB
to approximately 30 dB. Experiments show that the conditioned self-sensing schemes achieve
an excellent signal-to-noise ratio and can therefore be used to provide the feedback signal for
TM-AFM imaging.

@article{Ruppert2013b,
title = {A novel self-sensing technique for tapping-mode atomic force microscopy},
author = {M. G. Ruppert and S. O. R. Moheimani},
doi = {http://dx.doi.org/10.1063/1.4841855},
year = {2013},
date = {2013-12-01},
journal = {Review of Scientific Instruments},
volume = {84},
number = {12},
pages = {125006},
abstract = {This work proposes a novel self-sensing tapping-mode atomic force microscopy operation utilizing charge measurement. A microcantilever coated with a single piezoelectric layer is simultaneously used for actuation and deflection sensing. The cantilever can be batch fabricated with existing Micro Electro Mechanical System processes. The setup enables the omission of the optical beam deflection technique which is commonly used to measure the cantilever oscillation amplitude. Due to the high amount of capacitive feedthrough in the measured charge signal, a feedforward control technique is employed to increase the dynamic range from less than 1dB to approximately 35dB. Experiments show that the conditioned charge signal achieves excellent signal-to-noise ratio and can therefore be used as a feedback signal for AFM imaging.},
keywords = {MEMS, Smart Structures, SPM, System Identification},
pubstate = {published},
tppubtype = {article}
}

This work proposes a novel self-sensing tapping-mode atomic force microscopy operation utilizing charge measurement. A microcantilever coated with a single piezoelectric layer is simultaneously used for actuation and deflection sensing. The cantilever can be batch fabricated with existing Micro Electro Mechanical System processes. The setup enables the omission of the optical beam deflection technique which is commonly used to measure the cantilever oscillation amplitude. Due to the high amount of capacitive feedthrough in the measured charge signal, a feedforward control technique is employed to increase the dynamic range from less than 1dB to approximately 35dB. Experiments show that the conditioned charge signal achieves excellent signal-to-noise ratio and can therefore be used as a feedback signal for AFM imaging.